Working on codegen for if nodes.
Working on codegen for if nodes.

Need to motify the way BBs are created. I should create them with Block() and
only later insert them into the function with f.basic_blocks.append...

This ensures properly nested creation of BBs in case of nested conditionals,
the way it's done in the C++ code.

eliben/pykaleidoscope,thebusytypist/pykaleidoscope